SODIUM HYDROXIDE (NaOH) – REACH
Communication on uses and exposure scenarios
Based on the REACH Regulation a chemical safety assessment is needed for the substance
sodium hydroxide. To enable a chemical safety assessment the uses of sodium hydroxide have to
be evaluated and exposure scenarios have to be developed.
Hazards of sodium hydroxide
Sodium hydroxide is labeled as corrosive at concentrations of 2 % or higher. The concentration
of the substance, as it is placed on the market by the manufacturers, has a much higher
concentration than 2 % and therefore the commercialized substance is corrosive (R35 Causes
severe burns). The most common product is a liquid, which has a concentration of 50 % sodium
hydroxide in water.
Sodium hydroxide is an inorganic substance with a negligible vapour pressure. Exposure through
inhalation is therefore normally not an issue. Only when aerosols (solid or liquid) are formed
inhalation of sodium hydroxide could occur.
Uses
Sodium hydroxide has many different uses. Within industry it can be used for example to adjust
the pH, to produce biodiesel from vegetable oils, to clean bottles (food industry), to de-ink water
(pulp and paper industry), to dry air, to extract alumina (aluminum industry), to mercerize cotton
(textile industry), to peel leather, to peel vegetables, to manufacture chemicals (intermediate use),
to regenerate resins or to soften water. Consumer uses are for example paint stripping or to
unblock sinks. Clearly, these are only examples and more uses of sodium hydroxide do exist.
To describe the uses within REACH a use descriptor system has been developed. The guidance
document, which describes this system is available via internet:
http://guidance.echa.europa.eu/docs/guidance_document/Inforeq_CSR_R12_en.pdf
Because sodium hydroxide has so many uses and is used so widely it can potentially be used in
all sectors of use (SU) described by the use descriptor system (SU 1-23).
Sodium hydroxide can be used in many different chemical product categories (PC). It can be
used for example as an adsorbent (PC2), metal surface treatment product (PC14), non-metal-
surface treatment product (PC15), intermediate (PC19), pH regulator (PC20), laboratory chemical
(PC21), cleaning product (PC35), water softener (PC36), water treatment chemical (PC37) or
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extraction agent. However, it could potentially also be used in other chemical product categories
(PC 0 – 40).
Sodium hydroxide could be used according to the following process categories (PROC):
PROC1 Use in closed process, no likelihood of exposure
PROC2 Use in closed, continuous process with occasional controlled exposure
PROC3 Use in closed batch process (synthesis or formulation)
PROC4 Use in batch and other process (synthesis) where opportunity for exposure arises
PROC5 Mixing or blending in batch processes (multistage and/or significant contact)
PROC8 Transfer of chemicals from/to vessels/large containers at non dedicated facilities (?)
PROC9 Transfer of chemicals into small containers (dedicated filling line)
PROC11 Non industrial spraying
PROC13 Treatment of articles by dipping and pouring
PROC15 Use of laboratory reagents in small scale laboratories
The process categories mentioned above are assumed to be the most important ones but other
process categories could also be possible (PROC 1 – 27).
To assess the environmental exposure of substances environmental release categories (ERC)
have been developed for REACH. For sodium hydroxide the following environmental release
categories could be applicable:
ERC1 Manufacture of substances
ERC2 Formulation of preparations
ERC4 Industrial use of processing aids in processes and products, not becoming part of articles
ERC6A Industrial use resulting in manufacture of another substance (use of intermediates)
ERC6B Industrial use of reactive processing aids
ERC7 Industrial use of substances in closed systems
ERC8A Wide dispersive indoor use of processing aids in open systems
ERC8B Wide dispersive indoor use of reactive substances in open systems
ERC8D Wide dispersive outdoor use of processing aids in open systems
ERC9A Wide dispersive indoor use of substances in closed systems
The environmental release categories mentioned above are assumed to be the most important
ones but other environmental release categories could also be possible (ERC 1 – 11b).
Although sodium hydroxide can be used during the manufacturing process of articles, the
substance is not expected to be present in the article. The article categories (AC) do not seem
applicable for sodium hydroxide.
Operational conditions and risk management measures
Because sodium hydroxide is corrosive, the risk management measures for human health should
focus on the prevention of direct contact with the substance. For this reason automated and closed
systems should preferably be used for industrial and professional uses of sodium hydroxide. Due
to the corrosive properties appropriate skin and eye protection is required. Respiratory protection
is needed when aerosols of sodium hydroxide can be formed.
For environmental emissions to the aquatic compartment it is important to assure that the effluent
is neutralized within an acceptable range for local conditions before discharge to the environment.
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A significant pH increase of the aquatic environment due to an emission of sodium hydroxide
should be prevented.
Exposure scenarios
Because sodium hydroxide is a corrosive substance with a very low vapour pressure, the
operational conditions and risk management measures are similar for many different uses of
sodium hydroxide. For this reason the uses are grouped together for exposure assessment
purposes. Only a limited number of generic exposure scenarios are proposed, which are intended
to cover all uses. Please find hereafter the proposed list of exposure scenarios:
- manufacturing,
- industrial and professional use and
- consumer use.
It is proposed to develop separate scenarios for liquid and solid sodium hydroxide.
These three exposure scenarios for liquid and for solid sodium hydroxide, which are mentioned
before, cover a wide range of processes or uses, which means that they can be considered “use
and exposure categories” (see item 37 and 38 of Article 3 of the REACH Regulation). These
generic exposure scenarios are intended to cover all uses.
Communication between registrants (suppliers) and downstream users
Downstream users of sodium hydroxide are encouraged to verify if their product category,
process category and environmental release category of their uses are included in this document.
If not, please inform your supplier. The complete lists of product categories, process categories
and environmental release categories can be found in chapter R.12 of the REACH guidance
document (see internet link on page 1). The full list of use descriptors can be found in the excel
file:
http://www.eurochlor.org/upload/documents/document406.xls
It would also be useful to check if the proposed risk reduction measures are appropriate.
Downstream users who have additional specific information about operational conditions or risk
reduction measures could contact their supplier. In this way the information can be included in
the Chemical Safety Report and the extended Safety Data Sheet. It is the intention of the NaOH
REACH consortium to include all uses, which can be considered safe.
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